1. Field of the Invention
The present invention relates to a laminate made of two film materials wish different tear resistance values, and in particular to a laminate made of polyester and polyethylene.
2. The Prior Art
Laminates made of a polyester (PET) layer and a polyethylene (PE) layer demonstrate insufficient tear resistance. The tear resistance of the laminate material is significantly lower than the tear resistance of the polyethylene, even if the thickness of the polyethylene layer is much greater than the thickness of the polyester layer. Specifically, the tear resistance of the laminate material is determined by the low tear resistance values of the polyester. A corresponding behavior is also shown by laminates of other film materials that differ greatly with regard to their tear resistance, e.g. in the case of laminates made of oriented polypropylene (OPP) and polyethylene (PE).
It is an object of the present invention to improve he tear resistance of a laminate made of materials tea have very different tear resistance values.
This object accomplished, according to the invention, with a laminate in which the part of the laminate that is made from a film material with a high tear resistance is structured in multiple layers and has at least two layers made from this high tear resistance material. These layers are connected with one another with an adhesive layer having a low peel resistance. The peel resistance as set up so that the layers can be pulled off, i.e. peeled off one another. Preferably, the adhesive layer is structured so that the layers can be separated from one another with a peel force between 4 g/cm (3.9 N/m) and 120 g/cm (118 N/m). With the layer structure according to the invention, the tear strength of the laminate can be improved by many times. When using viscous adhesives for a non-elastomer bond between the layer, the multi-layer arrangement of the part of the laminate made from high tear resistance has the effect of more advantageously distributing the force introduced into the laminate cross-section.
It is practical if the part of the laminate that contains a film material with a high tear resistance is also connected with the layer that contains the other film material (which demonstrates a comparatively low tear resistance) by an adhesive layer with a low shear resistance.
Typically, the film material with a high tear resistance has a tear resistance measured according to Elmendorf of at least 80 g/xcexcm (784.8 N/mm) in the machine direction and of at least 120 g/xcexcm (1,177.2 N/mm) in the crosswise direction. The layer that contains the other film material preferably has a tear resistance of less than 0.8 g/xcexcm (7.85 N/mm) in the machine and crosswise directions.